Typically, heavy commercial motor vehicles, such as trucks, tractor-trailer combinations, buses, and other vehicles use a pneumatic brake system where brakes are actuated by compressed air generated from ambient air by a compressor engaged with the vehicle engine. When braking is needed in a moving vehicle, the compressed air is fed through conduits and controls to the brake actuation chambers of service brakes. This typically engages a diaphragm or piston that acts on a brake shoe and drum assembly, where braking torque is applied.
To keep a still vehicle from moving or to control an errant vehicle, spring brakes are employed as emergency/parking brakes. In these, an actuator includes a strong compression spring which applies the brake when air is released from the actuation chamber. Normally, spring brakes are pressurized with air during movement of the vehicle. One wall of the chamber, typically a diaphragm or piston, is movable and compresses the spring. Barring the application of fail-safe redundancy to prevent unintended catastrophic brake engagement, the loss of air pressure to the spring brake causes the brake to become mechanically engaged.
The brake systems of towed vehicles, such as trailers, are connected to the towing vehicle to receive compressed air from that vehicle so that the service brakes are applied in unison with those in the towing vehicle. Spring brakes are similarly fed from the towing vehicle and responsive to operator action.
Those skilled in the art will recognize the terms “service brake” and “service brakes” designate the brakes used under normal driving conditions by the application of compressed air and the terms are used in this and more expansive meanings herein. Similarly, those skilled in the art use the terms “spring brake” and “spring brakes” to designate the aforementioned types of emergency/parking brakes and the terms are used in this and more expansive meanings herein.
Innovation in brake system design for heavy commercial motor vehicles is constrained by a significant body of governmental regulations such as Federal Motor Vehicle Safety Standard FMVSS-121 (49 C.F.R. 571 et al.) and its Canadian counterpart CMVSS-121. The plethora of regulations require systems to be designed with fail-safe redundancies, minimum sizes for tanks serving as reservoirs of compressed air, features that prevent overpressurization of brake actuators, and fail-safe connections. Consequently, innovation comes in incremental steps to match newly issued regulations or minor mechanical improvements.
Therein, the typical advances have been to resort to an ever increasingly complex, costly, and difficult to install arrangement of air reservoirs, multiple pressure valves, pneumatic controls, and conduits providing selective application of compressed air while still maintaining the system in regulatory compliance.
FIG. 2 illustrates a typically complex conventional design for a tractor-trailer combination and the problems associated with such known designs. The advantageous embodiments of the present invention will be best understood in contrast with such a known more cumbersome design.
In the truck, interchangeably called the tractor, air compressor 1 is operated by the engine of the vehicle. When the compressor is loaded, e.g. engaged, it passes compressed air to air dryer 2 where moisture entrained air is removed by passing it over a desiccant bed. The dried compressed air is fed to supply reservoir 3c which in turn feeds it to primary reservoir 3a and secondary reservoir 3b. To protect reservoir 3a from overpressurization, safety valve 4 is provided and to protect reservoirs 3a and 3b from the loss of air pressure, check valves, e.g. one way valves, 5a and 5b are provided, respectively. Further, analog instrumentation 6 is provided for measuring reservoir 3c, and instrumentation 7a and 7b, usually affixed to the cabin dash, are provided to gauge air pressure in reservoirs 3a and 3b. When reservoirs 3a and 3b are pressurized to a predetermined level, pneumatic pressure causes electro-mechanical governor 8 to unload, e.g. disengage, compressor 1 to prevent uncontrolled pressure build-up in the system.
Foot brake valve 11 typically is a dual circuit type valve responsive to a treadle and plunger or pedal and plunger operated by the driver. During normal operation, when foot brake valve 11 is actuated, air is fed from reservoir 3b to the actuating chambers of the truck service brakes 12a and 12b via a plurality of valves and conduits. Simultaneously, compressed air is also fed to truck service brakes 13a and 13b of another axle via relay valve 14. There, service brakes 13a and 13b typically are disposed as combination brakes that also include parking brakes 15a and 15b. The actuating chambers of the truck service brakes convert air pressure to braking torque.
In the event that a failure in primary reservoir 3a or the supply lines from reservoir 3a occurs, the mechanical action of depressing foot brake valve 11 causes internal valves to feed compressed air from secondary supply reservoir 3b to the system instead from primary supply reservoir 3a. 
Pertinent to Federal safety regulations, the actuating chambers of truck parking brakes 15a and 15b typically include spring elements that engage the brake by forcing the braking pads in a friction bearing position. Thus, the circuit feeding the spring brakes is pressurized during vehicle movement. To disengage the brake during movement compressed air has to continuously exceed the spring forces in the brake. Typically, compressed air is fed by a circuitous route that includes sufficient redundancy to prevent unintended brake application through valves and conduits to brakes 15a and 15b. 
Multiple valve system such as this known system, typically include a plurality of valve types. Pressure protection valves maintain pressure in the air supply line between the steering and at least one steerable axle in the event of failure of a pressurized air reservoir of the vehicle. Such a function prevents automatic application of the spring brakes that are activated once the pressure in the air supply line drops below a certain reference pressure. Pressure protection valves are sometimes disposed in combination with check valves. Single check valves allow compressed air to flow in only one direction and are usually of the ball or disk valve type. Double check valves feed compressed air to one component from two sources of pressurized air. In this manner, both sources of pressurized air are able to control the recipient component.
For the operator-driver to place the spring brakes in a state to permit vehicle movement, air must be fed from primary reservoir 3a and secondary reservoir 3b to cabin dash manifold 16. As shown in FIG. 3, manifold 16 includes mechanical controls 30 and 31 and a plurality of entrance and exhaust ports 32 where a plurality of conduits 33 connect to the manifold requiring the conduit lines to be plumbed into the confined cabin space. Typically, control 30 is pulled to apply the parking brake, and conversely it is pushed to disengage the parking brake permitting compressed air to be fed into the actuating chambers of brakes 15a and 15b. 
To place the trailer braking system in operation the system must be charged with compressed air by operating control 32, shown in FIG. 3 as a push-pull switch, and combining the feed from the primary supply circuit with the feed from the secondary supply circuit at a check valve. The increased pressure overcomes two-way protection valve 17 feeding compressed air to the trailer when gladhand connectors 20c and 20d of the trailer mate with gladhand connectors 20a and 20b of the tractor, respectively. Connectors 20a and 20b are connected to mating gladhand connectors 20c and 20d and connected by conduits to relay valve 21 which is operably connected to reservoir 22. The reservoir is in turn operably connected through relay valve 21 to service brakes 23a, 23b, 25a, and 25b disposed with spring brakes 24a, 24b, 26a, and 26b, respectively. Relay valve 21 supplies pressurized air to, maintains pressure in, and releases pressurized air from the service brake chambers pursuant to control signals that are received from the tractor.
Similar to the tractor's parking/emergency brake circuit, the trailer's parking/emergency brake circuit is pressurized during vehicle movement to overcome the spring biasing in the trailer spring brakes. The trailer service brakes are activated when foot brake valve 11 is applied. Thus, compressed air is fed throughout the truck system and into the trailer system and via relay valve 21 to service the actuating chambers of the trailer service brakes. Hand brake valve 19, usually disposed on the steering column of the tractor, provides independent control of the trailer spring brakes when so desired by the operator.
From the foregoing description, it can be seen that to be in regulatory compliance, controls in a typical brake systems demand complex valve installations and interconnections. It can further be seen from the description that except for the electro-mechanical action of the compressor, compressed air is entirely managed by pneumatic controls. The complex interaction of controls depended on redundancies and charged pressures is necessary for regulatory compliance.
However, each valve and conduit inherently is associated with costs relative to design, installation, service, and parts inventory during vehicle manufacture and for servicing. While pneumatic controls in vehicles are generally effective as controller per se, such controls are inefficient since the controlled fluid media must be routed through the control. Thus, a plurality of conduits must be connected to the entrance and exhaust ports of the control to supply the compressed air and then feed it to the selected target. Consequently, the inherent limitations require that installation space must be reserved for control routing to accommodate the large bending radii of conduits, retaining fixtures that connect conduit to host vehicle, rigid conduit sections in corners and at sensitive locations, and protective insulating material of conduits. In turn, the significant number of parts needed for control routing incur manufacturing costs and lead to vulnerabilities in the manufacturing supply chain of the vehicle.
Cumulatively, these and other problems make installation and service of most pneumatic controls difficult in situations that place a premium on space, operator safety and comfort, and servicing accessibility. For example, in the cabin of a heavy vehicle valve and instrumentation controls must be fit into a confined dash space and may pose potential hazards to a driver. In the known brake system illustrated, placing the system of FIG. 2 in readiness requires the operator-driver to push or pull valve control switches in a dash mounted manifold control, illustrated in FIG. 3. Numerous air conduits must be connected to the manifold dash valves to permit the mechanical switching necessary to feed compressed air throughout the brake system by conduits and past mechanically operated pressure control valves.
It is also known, pneumatic controls are not flexible to accommodate changes in the physical limitations of the host vehicle. Thus, once the control routing of a brake system has been designed by a vehicle manufacturer redesign of the control routing becomes burdensome and expensive per se. Additionally, if one design has been successful, design changes may necessitate stocks of multiple part schemes resulting in burdensome parts inventory for multiple vehicle dimensions that would need to be maintained in repair facilities.
As is known that electronic controls overcome at least some of the disadvantages of pneumatic controls, namely reduced installation space, design and installation flexibility, ease in servicing, and parts efficiency. It is also known that controller area networks (CAN) effectively network and control mechanical devices through electronic controls. However, often individual electronic controls are simply substituted for individual mechanical controls leading to a hodge-podge of substitutions.
What is desired therefore is a system that simplifies the supply controls of a pneumatic braking system, that can be easily installed in a vehicle, that creates a more comfortable cabin environment for an operator, and that is more efficient in manufacturing, maintenance, and servicing. What is also desired is an electronic control system that allows further integration into other vehicle systems now known or to be developed.